What is the LIT file format?
.lit is the proprietary e-book format used by Microsoft Reader, first released in 2000. The name derives from "literature." Files use an ITOL/ITLS binary container - the same container family as Microsoft Compiled HTML Help (.chm) - holding XHTML-based content, CSS styling, embedded images, and metadata conforming to the OEBPS 1.0 (Open eBook) standard.
Two variants exist: DRM-free .lit files and ODRM-protected files. ODRM (Owner/Sealed DRM) ties a file to a specific Microsoft Passport account and, in its hardware-bound form, to a particular device. DRM-free .lit files can be opened in Calibre. DRM-protected copies cannot be read on a different machine without first removing the protection.
Microsoft Reader reached version 2.4.4 before being discontinued. LIT title sales ended when Ingram ceased distributing the format in 2011. No modern e-reader device or application natively supports .lit; the format has been superseded by EPUB.
If you have a DRM-free .lit file, Calibre can convert it to EPUB or other current formats. DRM-protected files are largely inaccessible today, as the tools that once removed LIT DRM (such as ConvertLIT) are unsupported and the Microsoft Passport infrastructure they relied on has changed significantly.
Security & safety
RISK: LOWLIT files are e-book containers - no executable code. Risk is very low. DRM-protected LIT files are tied to a Microsoft account; the license servers shut down in August 2012, so protected books cannot be activated on a new machine.
Format details
in a nutshell- LITCOIN / miscellaneous binary - .lit is occasionally used by niche tools for unrelated binary formats; context from db_name confirms Microsoft Reader e-book is the dominant meaning.
Programs that open LIT files
Windows2 apps
Microsoft Reader
Free Microsoft Reader 2.4.4 - discontinued August 30, 2012; license servers offline; DRM-protected books will NOT open. Historical reference only. 
Calibre
Open-source Add the LIT file to Calibre library (drag & drop or 'Add books'). Works only for DRM-free LIT files. To convert: right-click → Convert books → EPUB/PDF. 
macOS1 app
Calibre
Open-source Add DRM-free LIT file to Calibre; read in the built-in viewer or convert to EPUB/PDF. 
Linux1 app
Technical details
deep spec| Magic bytes | `49 54 4F 4C 49 54 4C 53` - ASCII string `ITOLITLS` at offset 0 |
| Container format | ITOL/ITLS - Microsoft Compressed HTML Help 2.0 derivative (same binary family as `.chm`) |
| Compression | LZX compression applied per content stream |
| Content standard | OEBPS 1.0 (Open eBook Publication Structure) - XHTML markup, CSS subset, GIF/JPEG/PNG images |
| DRM system | ODRM (Owner/Sealed DRM) - ties file to Microsoft Passport account; hardware-bound variant ties to specific device |
| DRM-free variant | DRM-free `.lit` files exist and are readable by Calibre for conversion to other formats |
| Byte order | Little-endian |
| Typical size | 200 KB - 5 MB |
| DRM integrity check | SHA-1 hash within ODRM envelope (DRM-protected files only) |
| Associated OS | Windows, Windows Mobile, Windows Phone (legacy) |
| Format status | Discontinued; Microsoft Reader officially retired in 2012, superseded by EPUB |
| MIME type | `application/x-ms-reader` |
| Released | 2000 (Microsoft Reader 1.0) |
| Latest version | Microsoft Reader 2.4.4 (final, circa 2009) |
LIT conversions
Community Q&A
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